1. Field of Invention
This invention relates to the field of all-plastic drums of the heavy-duty, industrial type for shipping and storing liquids, semi-liquids, as well as many other forms of bulk material.
2. Prior Art
In recent years, many different types of drums have been proposed, particularly for liquid and semi-liquid materials, such as plastic lined fiber or metal drums and all-plastic blow-molded drums. Drums having outer shells of fiber and metal, while providing needed strength and rigidity, also add considerable weight to the final product. In many cases, fiber shells are subject to deterioration if exposed to heat, cold, water, or ice for any extended periods of time.
All plastic blow-molded drums, while effective for shipping and storing materials, are limited in their ability to be mass-produced because of the requirement that they be subjected to considerably long cooling cycles in order to permit the resin to adequately harden and set following the blow molding cycle.
One of the drawbacks of any blow molding operation is the inherent non-uniformity of thickness of the walls of the ultimately formed drum with some portions of the drum having considerably more thickness than required while others possessing zones of weakness which may ultimately cause rupture and failure at these locations during drum use and abuse.
There have been attempts to provide an all plastic drum by assembling a pre-formed tubular body member with pre-formed top and bottom closures. The top and bottom closures were secured to opposite ends of the body member by the use of metal chimes. A drum of this construction is disclosed in U.S. Pat. No. 3,955,705 granted May 11, 1976. While a drum of this type has met with success, it will be apparent that the metal chime strips add weight to the product and also require additional manufacturing steps in order to complete the assembly of the finished product.